Multiple Sclerosis (MS) is a debilitating neuroimmunological and neurodegenerative disorder affecting over 400,000 individuals in the United States. Myelin loss, gliosis, and varying degrees of axonal pathology culminate in progressive neurological dysfunction including sensory loss, weakness, visual loss, vertigo, incoordination, sphincter disturbances, and altered cognition. The evidence for a genetic influence in MS is overwhelming but the etiology springs not from a single major gene, but from multiple genes acting either independently or interactively. This complexity has made the search for the responsible genetic variations difficult. A candidate gene approach identified allelic association with the HLA-DR2 allele but no other allelic associations have been confirmed. In the current funding cycle we completed a second-generation genomic screen and initial follow-up has identified one strong chromosomal linkage signal congruent with other studies. We also generated exciting data suggesting that the expression of clinical symptoms of MS is influenced by genomic variation(s) in or near APOE on chromosome 19q13. With the explosion of data from the human genome project, new methods of laboratory and statistical genetic analysis, and substantial expansion of our MS dataset, we can now take new approaches toward dissecting the complex genetics of MS. To achieve these goals, we propose five specific aims (1): To examine in detail chromosome 1q42 to identify the underlying MS risk gone; (2): To analyze SNPs in and near APOE for allelic associations to MS disease expression; (3): To test for association between MS and genes involved in oxidative stress; (4): To examine genes identified through expression analysis in MS tissues and acting in critical pathways; and (5): To test for gene-gene interactions. All analyses will take into account the known association with the HLA-DR2 allele seen in both our Caucasian and African-American datasets. We will genotype over 200 multiplex families, 1,500 Caucasian US singleton families, 1,000 Caucasian UK singleton families, 1,000 controls, and 1,000 African-American singleton families.